Most product certification bodies (or product certifiers) are accredited to ISO/IEC Guide 65:1996,[1] an international standard for ensuring competence in those organizations performing product certifications. The organizations which perform this accreditation are called Accreditation Bodies, and they themselves are assessed by international peers against the ISO 17011 standard.[2] Accreditation bodies which participate in the International Accreditation Forum (IAF) Multilateral Agreement (MLA)[3] also ensure that these accredited Product Certifiers meet additional requirements set forth in "IAF GD5:2006 - IAF Guidance on the Application of ISO/IEC Guide 65:1996".[4]

A product might be verified to comply with a specification or stamped with a specification number. This does not, by itself, indicate that the item is fit for any particular use. The person or group of persons who own the certification scheme (i.e., engineers, trade unions, building code writers, government, industry, etc.) have the responsibility to consider the choice of available specifications, choose the correct ones, set qualification limits, and enforce compliance with those limits. The end users of the product have the responsibility to use the item correctly. Products must be used in accordance with their listing for certification to be effective.

Product certification is often required in sensitive industry and marketplace areas where a failure could have serious consequences, such as negatively effecting the health and welfare of the people or person using that product. For example, certification is stringent in aerospace applications, since the demands for low weight tend to lead to high stress on components, requiring appropriate metallurgy and accuracy in manufacturing. Other sensitive product area examples include food, pharmaceuticals, healthcare products, dangerous goods, and products which have RF emissions such as computers and cellular telephones.

The process for certification of a product is generally summed up in four steps:

Decision (does a second review of the product application concur with the Evaluation)

Surveillance (does the product in the marketplace continue to meet qualification criteria)

In many instances, prior to applying for certification, a product supplier will send a product to a testing laboratory (some certification schemes require the product to be sent out for testing by the product certifier instead). When the product to be certified is received at the testing laboratory, it is tested in accordance with the laboratory's internal procedures and with the methods listed in the test standards specified by the certification scheme. The resulting data collected by the testing laboratory, and is then forwarded either back to the manufacturer, or directly to the product certifier.

The product certifier then reviews the product supplier's application information, including the testing data.[1] If the certifier's evaluation[1] concludes that the test data shows that the product meets all required criteria as listed in the certification scheme, and the decision maker(s) of the product certifier concur with the evaluation,[1] then the product is deemed "certified" and is listed in a directory which the Product certifier is required to keep.[1] ISO Guide 65 requires[1] that the final decision to grant or not grant certification be made only by a person or group of persons not involved in the evaluation of the product.

Products often need periodic recertification, also known as surveillance. This requirement is typically identified within the certification scheme that the product is certified to. Certification bodies may require product suppliers to perform some sort of surveillance activity,[1] such as pulling sample products from the marketplace for testing,[6][7] in order to maintain their "listed" or "certified" status. Other examples of Surveillance activities include surprise audits of the manufacturing plant, supervision of the manufacturing and/or testing process,[8] or a simple paperwork submittal from the supplier to the product certifier to ensure that the certified product has not changed. Other causes for recertification may include complaints issued against the product's functionality which would require removal from the marketplace, and expiration of the original certification. These lists of examples are by no means all inclusive.

Some certification schemes, or the product certifiers which operate those Schemes, may require that the product supplier operate a Quality Management System registered to ISO 9000, or that the testing be performed by a laboratory accredited to ISO 17025.[9] The decision to set these requirements is most often made by the person or group which owns the Certification Scheme.

Certified products are typically endorsed with a certification mark provided by the product certifier. Issuance of a certification mark is at the discretion of the individual product certifier. ISO Guide 65 does not require the product certifier to offer a certification mark in the event that a certificate is offered. When certification marks are issued and used on products, they are usually easy to see and enable users to track down the certification listings to determine the criteria that the product meets, and whether or not the listing is still active.

Product certifiers may choose to include much more information than that listed above, but ISO Guide 65 specifies the bare minimum which must be made available regarding the certification status of a product.

These listings are typically used by an Authority Having Jurisdiction (AHJ), such as a municipal building inspector, fire prevention officer, or electrical inspector, to compare the product's use or installation with the intent of the rating by testing. In order to comply with the code, the product listing must be "active", as products and companies can become "de-listed" due to re-testing showing that a product no longer meets qualification criteria, or a business decision by the manufacturer.

The International Accreditation Forum (IAF) has a listing of all recognized Accreditation Bodies whose accreditations to the ISO Guide 65 standard are deemed equivalent. From the IAF MLA informational page:[10]

"IAF is encouraging more of its members to join the MLA as soon as they have passed a rigorous evaluation process to ensure that their accreditation programs are of world standard. The consequence of joining the IAF MLA is that conformity assessment certificates issued, within the scope of the IAF MLA, by conformity assessment bodies accredited by any one of the members of the IAF MLA will be recognised in the world wide IAF program."

Most countries only have a single Accreditation Body representing their economy in the IAF MLA. The two exceptions are the United States with American National Standards Institute (ANSI), American National Standards Institute - American Society for Quality National Accreditation Board (ANAB, a subdivision of ANSI), American Association for Laboratory Accreditation (A2LA), and International Accreditation Service (IAS) as signatory members, Europe with the TUV Technischer Überwachungs-Verein, English: Technical Inspection Association, and Korea which is represented by Korea Accreditation Board (KAB) and Korean Accreditation System (KAS). These listings are current as of March 2012, but will likely change in the future as more Accreditation Bodies undergo the required peer evaluations in order to become signatory members of the MLA.

Each Accreditation Body is required to keep a listing of those organizations it accredits, as well as a Scope of Accreditation which details the activities that the organizations can perform, whether that be testing, inspection, or product certification.[2]

Accreditation Bodies routinely audit[2] the Product Certifiers whom they have accredited in order to determine if the performance or actions of the organization have changed and do not meet the requirements of the Accreditation Body and the International Standards they are to conform to.

North America's nuclear industry is exempt from mandatory certification[citation needed]. This has allowed situations leading to large amounts of remedial work, especially for fireproofing of electrical circuits (circuit integrity) between nuclear reactor and control rooms in the U.S. In this case, submitors were permitted to dictate not only their test procedures, but also to construct test specimens in their own facilities, prior to fire tests on the part of laboratories. The primary example of this situation is the Theromo-Lag Scandal, which came about as a result of disclosures by whistleblowerGerald W. Brown to the Nuclear Regulatory Commission as well as watchdog groups, members of US Congress, and the press.

In Germany, the accredited testing organizations routinely audit manufacturing locations and submit quality control test results to DIBt. While the German laboratories do not possess process standards, their methodology can uncover changes in the nature and quality of ingredients, as DIBt establishes very clear tolerances for performance[citation needed].

Where product certification is optional, one must rely on the ethics of the manufacturer that the item being sold is identical to the item that was tested, and that the item that was tested was in fact installed the way the test report reads. The test report by itself also does not afford its bona fide interpretation in terms of the tolerances that a certification listing would provide.